Cathode for electric discharge devices



March 13, 1934. H, SIMON CATHODE FOR ELECTRIC DISCHARGE DEVICES FiledAug. 12, 1931 Inventor. Hellrnut Simon,

by 1 His Attorney.

Patented Mar. 13, 1934 STAT Z 1 S PATE T OFFICE CATHODE FOR ELECTRICDISCHARGE DEVICES Hellrnut Simon,

Berlin-Charlottenburg,

Ger-

many, assignor to General Electric Company, a corporation of New YorkApplication August 12, 1931, Serial No. 556,709 In Germany August 25,1930 6 Claims.

. The present invention relates to cathodes for electric dischargedevices and more particularly to cathodes designed to carry largecurrent at relatively low voltage.

Heavy current cathodes of large power tubes are sometimes constituted ofmetallic strips having a serpentine, looped or spiral configuration andpresented edgewise to the anode. These shapes are desirable in order toobtain large cathode surfaces in relatively small spaces and to minimizeradiation of heat. It is found in practice that when cathodes of thischaracter are heated, the folds or convolutions, upon expansion,sometimes tend to distort in shape and change the relative position ofthe various portions of the cathode with respect to one another, whichcauses deleterious operating effects.

An object of the present invention is to pro- :vide an improvedarrangement for holding a cathode structure of the type referred torigidly in shape under heated and unheated conditions. This object isattained in brief by bracing the various parts of the cathode with tiewires constituted of refractory material, also of high mechanicalstrength and high resistance, so as not to cause excessive current loss.The invention will be better understood when reference is made to thefollowing description and accompanying drawing in which Fig. 1represents a View in perspective of the improved cathode; Figs. and 3show modified structures, and Fig. 4 is cross-section taken on line 4-4of Fig. 3.

Referring to Fig. l, numeral 1 designates a strip form of cathodeconstituted of a number of parallelly aligned portions folded or bentback on one another and terminating in loops 2. The cathode may befabricated of any suitable metal, for example, nickel, and, if desired,coated with an electronically active material in any well known andsuitable manner. The loops 2 grip metal uprights 3 which are bent at thetop to form horizontal members i extending in opposite directions, asshown. The members 4 are tied rigidly together by means of one or morewires 5 pulled or stretched sufficiently tight so as to cause horizontalmembers 4 to rest against the vertical surfaces of the two outerportions of the cathode.

The wires 5 are preferably made of a tough, high refractory metal, suchas tungsten, in order that sufficient tension may be applied underheated conditions without breakage. The wires are also of small gaugeand of high resistance in order to introduce sufficient resistance tothe current which flows in parallel to the current through the cathodeproper. There are metals, including the nickel referred to, out of whichthe cathode can advantageously be made,

which produce ample electron emission at low temperatures so thatsuitable materials, such as iii) tungsten are abundantly available forthe bracing wires which have sufficient and dependable strength at theoperating temperature of the cathode.

It is evident that the is such as to preclude cathode as a whole, or

structural arrangement any movement of the the individual portionsthereof, in a direction normal to the length of each convolution becausethe distance between the support members 4 is rigidly fixed by the Asthe cathode is heated, the resulting wires 5.

expansion is taken up by a lengthening of the individual convolutionsalong their greatest dimension and to some extent by a change in thedistance between the juxtaposed portions of the However, the generalshape of strip material.

the electron emission surface remains substantially the same afterheating as before and the electrical characteristics of the tube inwhich such a cathode is used remain constant under 80 variable operatingconditions. It is evident that the wires 5 also impart considerablemechanical strength to the cathode as a whole, and if de sired, may besecured in any suitable manner as by welding, to intermediate portionsthereof in order to provide additional support. The uprights 3 may beextended through the of the tube in order to support the cathode metalpress Withtrons are emanated from both sides of the strip,

thereby to provide a tube of very low impedance in the current-carryingdirection.

In Fig. 2 the arrangement is somewhat similar to that shown anddescribed in connection with Fig. 1, except that the uprights 3terminate in vertical portions and lack the horizontal bers 4. andsupported between the two outermost The wires 5 in this case arestretched memedges of the cathode and, as in the case of Fig. 1, may bewelded or otherwise secured to intermediate portions of the cathode, ifdesired.

Figs. 3 and i show an arrangement particularly suitable for heavy andlong cathode strips. In this arrangement, the individual lengths of thestrip are braced between two or more oppositely extending diagonal wires5, which present a strong lateral supporting network.

These braces conveniently may be formed from a continuous length ofwire, wound tightly and bent over the diagonally adjacent edges of thestrip portions. are shown as metal members of rectangular cross-sectionwhich are rigidly secured as by weldingQto the face of the outermostconvolutions of the strip. It is apparent in this embodiment, that thewires 5 are bent sharply about the edges of the strip so that it is notnecessary to weld the wires to the edges, as in the case of the twopreceding figures, altho the welds may be employed, if desired. It isalso evident that more than one brace wire may be employed in any of theembodiments and if desired, such wires may start and terminate at bothedges of'the strips. Thus in Fig. 2, there are shown two pairs of wires,one pair lying along the upper edge of thestrip cathode and the otherpair secured to the lower edge thereof. In Figs. 3 and 4, one pair ofsupport wires starts at the upper'edge of one of the outermost portionsof the cathode and terminates at the upper edge of the. other outermostportion, while a second pair of support wires starts at the lower edgeof one of said portions and terminates at the lower edge of the other ofsaid portions.

While I have described my invention in connection with a serpentine orlooped form of cathode, it is to be understood that the bracing wiresmay advantageously be used with cathodes of all configurations where twoor more portions of a strip are in juxtaposed relation. Thus, theinvention has application to the spiral as well as to the helical typeof cathode, in which the bracing or support wire may be secured in anysuitable manner to one or more pairs of the con volutions.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is: 1. A cathode for an electron discharge device comprising ametallic strip member bent back on itself to constitute a plurality ofjuxtaposed portions and means for holding said portions rigidly in placewhereby the cathode as a whole is precluded from distortion duringoperation and manufacture, said means comprising a wire stretchedbetween the extreme end portions of the cathode.

2. A cathode for an electron discharge device comprising a metallicstrip member bent back on The vertical uprights 6 in this figure Iitself to constitute a plurality of juxtaposed poitions, and means forholding said portions rigidly in place whereby the cathode as a whole isprecluded from distortion during operation and manufacture, said meanscomprising a wire stretched between the extreme end portions of thecathode and secured to intermediate portions thereof.

3. A cathode for an electron discharge device comprising a metallicstrip member bent back on itself to constitute a plurality of juxtaposedportions adapted to emit electrons, a pair of rigidsupport rods, theextreme end portions of the cathode being provided with loops whichembrace the rods, and means, comprising a wire stretched between saidrods, for rigidly .holding said juxtaposed portions in place.

4. A cathode for an electron discharge device comprisingia metallicstrip member bent back on itself to constitute a plurality of juxtaposedportions adapted to emit electrons, a pair of rigid support rods, theextreme end portions of the cathode beingprovided with loops whichembrace the rods, and means, comprising a Wire stretched between saidrods, for rigidly holding said juxtaposed portions in place, said meanscomprising a wire stretched between diagonally opposite edges of therespective portions.

5. A cathode for an electron discharge device comprising a metallicstrip member constituted of a plurality of convolutions in juxtaposedfiatwise relation, and means for holding said convolutions rigidly inplace whereby the cathode as a whole is precluded from distortion duringoperation and manufacture, said means comprising an elongated member ofrefractory metal and of relatively high resistance secured to all ofsaid ccnvolutions.

6. A cathodefor an electron discharge device comprising a nickel stripmember constituted of a plurality of convolutions in juxtaposed fiatwiserelation, said member being coated with an electronically activematerial, and means for holding the convolutions rigid with respect toone another whereby the cathode as a whole is precluded from distortionduring operation and manufacture, said means comprising a tungstenwire'oi relatively small gauge secured to all of said ccnvolutions.

HELLMUT SIMON.

